Benefits 5 (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Pension member
Benefits [Line Items]
Discount rate	5.35%	5.82%	6.05%
Expected return on plan assets:
Tax exempt accounts	8.25%	8.25%	8.50%
Rate of compensation increase	3.02%	3.24%	3.24%
OPEB member
Benefits [Line Items]
Discount rate	5.36%	5.85%	6.05%
Expected return on plan assets:
Tax exempt accounts	7.00%	7.00%	7.00%
Taxable accounts	4.50%	5.00%	5.00%